The present invention generally relates to vehicle coolers, and in particular to the design of fluid conveying tubes included in such coolers.
One type of vehicle cooler, which is, for instance, disclosed in EP-A1-0 590 945 and which is joined by brazing, comprises a heat exchanger assembly which comprises on the one hand a row of flat fluid conveying tubes, which are juxtaposed to be passed by a first fluid, for instance, liquid circulating through an engine block and, on the other, surface-enlarging means arranged between the tubes and adapted to be passed by a second fluid, e.g. cooling air. Each tube has opposite large faces, to which the surface-enlarging means are applied and which form the primary heat exchanging sides of the tube. Since for reasons of strength the large faces of the tubes cannot have an optional width, the heat exchanger assembly is generally made up of several parallel rows of tubes, which are successively arranged in the flow direction of the second fluid through the heat exchanger assembly. Therefore, between each pair of rows there is a dead zone in which there is no heat exchange between the fluids. This dead zone can consist of up to 10-15% of the total depth of the heat exchanger assembly.
In order to increase the heat exchanging capacity of the vehicle cooler, it is known to provide each tube with several internal, parallel channels or ducts, which are mutually separated by a thin partition wall. The width of the tubes can thus be increased while maintaining the strength, and the vehicle cooler can be formed without said dead zone. Such a xe2x80x9cmultichannel tubexe2x80x9d is, for instance, known from EP-B-0 646 231.
There is, however, a constant need of improving the capacity of heat exchange in vehicle coolers, especially as there is limited space for vehicle coolers in today""s vehicles at the same time as the need for cooling is increasing, in particular in trucks. An improved capacity of heat exchange can be used to increase the cooling efficiency of a cooler having a given size or to reduce the size of a cooler having a given cooling efficiency.
It is an object of the invention to provide a fluid conveying tube and a vehicle cooler which for a given size have a better capacity of heat exchange than ordinary constructions.
It is also an object to disclose a simple technique of manufacturing such a fluid conveying tube at a relatively low cost and with a low degree of rejection.
These and other objects, which will appear from the description below, have now been achieved by means of a method and a device for manufacturing according to appended claims 1 and 5, respectively, as well as a fluid conveying tube and a vehicle cooler according to appended claims 10 and 14, respectively. Preferred embodiments are defined in the dependent claims.
The surface structure which is formed on the inside of the fluid conveying tube serves to break up the laminar boundary layer which has an insulating effect and which tends to form adjacent to the primary surfaces of the tube in the fluid flowing through the tube. Thus, the surface structure contributes to further improving the capacity of heat exchange of the tube, in particular at low flow rates of fluid through the tube, without any substantial increase of the pressure drop in the fluid flowing through the tube.
By the inventive manufacturing technique, the tube can be formed in one piece starting from a blank of metal material in a simple and cost-efficient manner.
According to a particularly preferred embodiment of the inventive manufacturing technique, the blank is provided with the surface structure only after the forming of two upright edge portions along two opposite edges of the blank. This minimises the risk of irregularities occurring in the outer edges of the blank during the forming of the surface structure on the surface of the blank, because the material of the blank has a certain tendency to skew when forming the surface structure. Since the outer edges of the blank are subsequently brought into abutment against the web portion for defining the ducts, such irregularities could make it necessary to reject the tube due to leakage between the ducts.